Float is a measure of the amount of ‘spare’ time that is available in addition to the time required to perform a given activity.
There are three different types of float:

  1. Total float
  2. Independent float
  3. Interference float

Total Float

Total float is the maximum length of time available to extend or delay an activity without causing following activities to be delayed. The total float for an activity is calculated as follows:

total float = latest end time – earliest start time – duration

Independent Float

Independent float is the amount of spare time that is only available to one activity. If the spare time available to one activity could also be used for another activity then it is not independent.

independent float = earliest end time – latest start time – duration

Interference Float

interference float = total float – independent float